I find the face detection feature quite good and the camera is quick too focus and shoot so its a case of if face is detected and you've got a potential shot your likely too get a in focus shot if you press that shutter button

I tend too have the continuous shooting mode on and will take say 4-5 in a photo just incase one of my kids blink etc:
If child is moving it might be worthwhile using the AFC type setting.
Apart from the above you can only raise the high iso too get that faster shutte speed too stop any blurred photo's but i like fast glass taking photo's of my kids so primes are the cheaper way too go on average for that like a 20mm f1.7 or 45mm f1.8 unless you want go for paying out for the 12-35mm f2.8 or 25mm f1.4
all above based in my opinion